Mr Mundell admitted to having reservations about the draft Brexit deal the Prime Minister has agreed with the European Union but said other alternatives were “even more unpalatable”. Speaking at a gathering of Scottish Conservatives in Falkirk, Mr Mundell praised Theresa May for the strength of character she had shown this week, as well as her sense of public duty and “sheer decency in the face of an unprecedented onslaught by detractors and the media”. He said: “She is tackling an issue of epic proportions, on which she can never please everyone, and she is doing her very best to find a way through.

“Let me be quite clear, if it comes to a confidence vote, she will have mine.”

Mr Mundell also launched a scathing attack against Scotland’s First Minister Nicola Sturgeon, accusing her of using Northern Ireland’s troubled past in attempts to increase support for Scottish independence.

He raged: “This week she reached a new low with her crass demands for Scotland to be equated with Northern Ireland.

“It confirmed that nothing is off limits now for Nicola Sturgeon – the sensitivities and unique circumstances of Northern Ireland, its geography, history and culture can be cast aside, if there is some opportunistic political point to be made.”

Mr Mundell added: “Scotland’s circumstances are nothing like those of Northern Ireland.

“Even the SNP used to acknowledge that, speaking out to have the Belfast Agreement upheld, but now none of that seems to matter any more, compared to the opportunity for tomorrow’s headline, one more seed of division, one more step however achieved on the road to independence.

“We, and Scotland, need to be on notice – Scottish politics just got a whole lot uglier. There is nowhere Nicola Sturgeon won’t go.”

The Scottish Secretary also told the gathering of ministers he will continue to press for reassurances the UK would leave the EU Common Fisheries Policy in December 2020.

Earlier this week British fishermen warned they were “suspicious” of the Prime Minister’s Brexit deal, with the small print of the proposed agreement suggesting they may be forced into regulations similar to that of the EU’s Common Fisheries Policy.

Fishermen in the UK already feel they have been deeply let down by the Government after the announcement of the implementation period effectively kept the industry under the control of the EU’s controversial Common Fisheries Policy until 2020.

But, the text in the ‘political declaration on the future relationship’ suggests that while Britain will be an “independent coastal state”, future cooperation on the development of measures “for the conservation, rational management and regulation of fisheries” will be done in a “non-discriminatory manner”.

Fishing for Leave said: “It is vital to remember that the disastrous transition and Chequers everyone was horrified by is still the deal, no matter what lipstick Downing Street spin onto a pig. Resolving the final five percent of a stinker doesn’t make it stinkless.

“The transition still means obeying all EU law, allowing the EU to enforce detrimental laws to massacre what’s left of the British fleet.

“This would allow the EU to cite international law to claim the ‘surplus’ resources Britain would no longer have the fleet to catch.

“If Mrs May has capitulated to EU demands to sacrifice fishing for this deal it is even more reprehensible. MPs in coastal constituencies and beyond will be massacred.

“Being a free, sovereign nation after the short term of separation is a far bigger boom than staying shackled as a vassal state to a failed EU we voted to Leave.”